The meanings of certain acronyms and abbreviations used herein are given in Table 1.
TABLE 1Acronyms and AbbreviationsAAAAuthentication, Authorization, and AccountingFCCHDFast Channel Change High DefinitionGOPGroup of PicturesHDHigh DefinitionIPInternet ProtocolMPEG-2Motion Picture Experts Group 2MPEG2-TSMotion Picture Experts Group 2 Transport StreamonidOriginal Network IdentifierPCRProgram Clock ReferenceSDStandard DefinitionsidStation IdentifierSTBSet-Top BoxSVGScalable Vector GraphicstsidTransport Stream Identifier
As digital television transmission has replaced analog broadcasts, viewers have found that the advantages of the newer mode are offset by a relatively long latency period when changing channels, as compared to the nearly instant response of a traditional analog tuner. This is a consequence of motion-compensated video encoding schemes, of which the well-known MPEG-2 standard is exemplary. The following international standards and specifications are particularly relevant to the understanding of the disclosure of the present invention: ITU-T Specification H.264 (March 2005), Advanced Video Coding for Generic Audiovisual Services; ISO/IEC 13818-1, Information Technology—Generic Coding of Moving Pictures and Associated Audio Information: Systems (Second Edition, 2000).
A video sequence known as a “group of pictures” (GOP) begins with an I-Frame, which is an independently decodable frame. The I-frame is followed by zero or more “predicted frames” known as P-frames and B-frames, which are encoded relative to the I-frame and/or one another, and generally cannot be decoded unless the I-frame is known. In other words, the GOP is decodable only once the I-frame has become available to the decoder.
A channel change request may occur randomly in the course of an MPEG-2 stream. It therefore is generally unaligned with the current I-frame. Hence, decoding of a new MPEG-2 stream is delayed until arrival of a new I-frame. This delay can be many seconds in duration, particularly when there is little motion occurring in the image being transmitted. The delay in video presentation may be increased even more by inherent latencies within the decoder. The result, if not compensated in some manner, is user dissatisfaction.
U.S. Pat. No. 7,562,375 proposes to change channels in a digital video environment by configuring a server to retain at least one independent frame for each video channel of multiple video channels that are being distributed using multicast communications. The server is adapted to respond to channel change requests from clients by transmitting the retained independent frame of a requested video channel to a requesting client using unicast communication.
U.S. Pat. No. 7,430,222 discloses facilitating a fast channel change by receiving and decoding a unicast acquisition media stream that corresponds to a soon-to-be requested target multicast media stream. This occurs before requesting the target multicast media stream of the new channel. Once the transmission of the unicast stream is caught up with the multicast stream, the unicast acquisition stream is spliced to the target multicast media stream.